Overall, the existing research suggests that children in foster care have more compromised developmental outcomes than children who do not experience placement in foster care.31 However, there is considerable variability in the functioning of foster children, and it is difficult to disentangle the multiple preplacement influences on foster children from those that result from the foster care experience itself. Children in foster care are biologically vulnerable to many poor developmental outcomes, due to genetic factors, prenatal substance exposure, and other physical health issues. Many of these children experienced trauma prior to foster care entry, which has been documented to have a major impact on children's outcomes across developmental domains.

Additionally, many scholars argue that the risk factor leading to negative outcomes is not foster care per se but the maltreatment that children experience beforehand. For example, in the NSCAW study, foster children with experiences of severe maltreatment exhibited more compromised outcomes.32 Other scholars suggest that foster care may even be a protective factor against the negative consequences of maltreatment.33 Similarly, it has been suggested that foster care results in more positive outcomes for children than does reunification with biological families.34 Further, some studies suggest that the psychosocial vulnerability of the child and family is more predictive of outcome than any other factor.35 Despite these caveats, the evidence suggests that foster care placement and the foster care experience more generally are associated with poorer developmental outcomes for children.

The Foster Care Experience and Developmental Outcomes

Many studies have pointed to the deleterious impact of foster care on children's physical health, cognitive and academic functioning, and social-emotional wellbeing. In the area of physical health, pediatric and public health scholars have documented that foster children have a higher level of morbidity throughout childhood than do children not involved in the foster care system. First, foster children are more likely to have perinatal experiences that compromise their physical health and overall development. For example, there has been a dramatic increase in the number of children entering foster care due to prenatal substance exposure.36 The negative effects of substance exposure on the fetus and developing child have been extensively documented, although scholars emphasize the variability in outcomes as well as the contribution of multiple ecological factors to outcome.37

Foster children are also more likely to have growth abnormalities and untreated health problems.38 Despite the trend in these data, some scholars have suggested that the negative health outcomes attributed to foster children are not distinct from those found among children living with their impoverished biological families. Although scholars have highlighted the fragmented system of health care for foster children, they also acknowledge an increased sensitivity to foster children's medical issues on the part of health care providers.39

In the area of cognitive and academic functioning, NSCAW documented that the majority of foster children scored in the normal range on cognitive and academic measures, although a higher proportion than would be expected in the general population were found to have delayed cognitive development and compromised academic functioning. For example, findings from NSCAW indicate that more than onethird of infants and toddlers in the One-Year Foster Care Sample and one-half in the Child Protection Sample scored in the delayed range on a developmental screener. In both samples, 7% of school-age children scored in the clinical range on a cognitive test, and 13% scored in the delayed range on a language test.40 These data corroborate findings from smaller studies that point to developmental and cognitive delays in this population of children.41 However, foster children scored in the same ranges as similarly high-risk children who were not in out-of-home placement (for example, children in poverty).

Regarding academic achievement, some studies have found that foster children perform more poorly on academic achievement tests, have poorer grades, and have higher rates of grade retention and special education placement.42 The poorer academic functioning of foster children may not be attributable to their foster care experiences per se but to their pre–foster care experiences such as poverty and maltreatment. Additionally, lower school attendance of foster children due to placement instability may be a contributor to their poor school functioning.

On social-emotional measures, foster children in the NSCAW study tended to have more compromised functioning than would be expected from a high-risk sample.43 Moreover, as indicated in the previous section, research suggests that foster children are more likely than nonfoster care children to have insecure or disordered attachments, and the adverse long-term outcomes associated with such attachments.44 Many studies of foster children postulate that a majority have mental health difficulties.45 They have higher rates of depression, poorer social skills, lower adaptive functioning, and more externalizing behavioral problems, such as aggression and impulsivity.46Additionally, research has documented high levels of mental health service utilization among foster children47 due to both greater mental health needs and greater access to services. Some scholars suggest that the poor mental health outcomes found in foster children are due to a variety of factors beyond their foster care experiences. These children may be biologically predisposed to mental illness and may have experienced traumas that have set them on a path of mental health difficulty.48

Placement Characteristics and Developmental Outcomes

The type of placement and the stability of that placement influence child outcomes. Research has shown that the majority of foster children are placed in foster families. A rapidly growing trend is the kinship placement of children. For example, in the NSCAW study, 58% of children who had been in foster care for one year were placed in nonrelative foster care, and 32% were placed in kinship care. The existing research on the effects of kinship care on child developmental outcomes are mixed. Some studies have documented that children in kinship care tend to have higher functioning than those in unrelated foster homes, but this may be a function of their being better off prior to placement with kinship care providers.49Another study, however, found that adults who had longer durations of kinship care as children had poorer outcomes than those who were in unrelated foster care.50

A much smaller proportion of children in the NSCAW study (9%) were placed in group homes or residential care. Such placements are more often used for adolescents and children with serious mental or physical health difficulties.51 Overall, the evidence suggests that group home placement is deleterious to children.52 Children in group care in the NSCAW study had poorer developmental outcomes than their counterparts in family environments, but they also had more intense needs at placement entry.53 In a study comparing young children reared in foster family homes to those in group homes, children in group care exhibited more compromised mental development and adaptive skills but similar levels of behavioral problems.54

The research also suggests that placement instability is associated with negative developmental outcomes for foster children. Changes in placement or disruption rates are related to the length of the child's foster care stay,55 the age of the foster child, and the functioning of the foster child (for example, mental health).56 The quality of the parent-child relationship and the caseworker- foster parent relationship also influences placement stability. Most foster children experience only one to two placements. However, report data indicate that one-third to two-thirds of foster care placements are disrupted within the first two years.57

The type of placement also contributes to placement stability.58 Children in kinship care tend to experience more stability (that is, fewer placement disruptions),59 although high disruption rates are found in kinship situations with vulnerable children and/or families.60 Placement stability for children in group care varies depending on child age and needs. For example, adolescents in group care typically have more stable placements than younger children. In contrast, very young children in group care experience a higher number of moves due to attempts to secure less-restrictive placements for them.61

It is difficult to disentangle whether placement stability predicts developmental outcomes or if children with developmental difficulties are more likely to experience multiple placements. For example, one study suggests that children's developmental delays may lead to multiple placements and also may be a consequence of multiple placements.62 Further, most studies examining the effects of placement instability are not methodologically rigorous. Nevertheless, many studies suggest that placement instability leads to negative outcomes for children. Children in the NSCAW study with multiple placements had more compromised outcomes across domains than children who experienced greater placement stability.63 In another study of a large group of foster children, the number of placements children experienced predicted behavioral problems 17 months after placement entry.64 Other studies have reported that placement instability is linked to child behavioral and emotional problems, such as aggression, coping difficulties, poor home adjustment, and low self-concept.65 Relatedly, children's perceptions of the impermanency of their placements have also been linked to behavioral difficulties.66